Optical and millimeter wave fusion bidirectional transmission system and method based on optical heterodyne

Abstract

The application relates to a kind of optical and millimeter wave fusion bidirectional transmission system and method based on optical heterodyne, and belongs to the technical field of space optical communication.The application generates single sideband optical signal by means of optical heterodyne method, provides single sideband light source with carrier for space optical link and millimeter wave link, realizes multiplexing of relevant devices between the transmitting end of two links, between the receiving end and between the receiving end of space optical link and the transmitting end of millimeter wave link, and reduces the structural complexity of fusion bidirectional system.The transmission system can be divided into isomorphic bidirectional transmission mode and heterogeneous bidirectional transmission mode.In isomorphic bidirectional transmission mode, photodetector is time division multiplexed by space optical link and millimeter wave link.In heterogeneous bidirectional transmission mode, two light signals sharing photodetector completely overlap in frequency domain, and the decomposition of two signals is realized by prior information method.The application reduces the structural complexity of system by device multiplexing design, and promotes the development of fusion transmission in space-based and air-based network.

Description

Technical Field

[0001] This invention belongs to the field of space optical communication technology, and relates to a two-way transmission system and method based on optical heterodyne and millimeter wave fusion. Background Technology

[0002] With the rise of data services requiring massive bandwidth, such as cloud computing, online video, and virtual reality, user demand for high-speed wireless connectivity is growing exponentially, while existing traditional wireless networks are increasingly unable to meet the growing frequency band requirements. Against this backdrop, Free Space Optical (FSO) communication and millimeter-wave communication have demonstrated enormous development potential. FSO communication transmits information in free space via lasers, achieving high-speed and secure data transmission without spectrum licensing, and is therefore widely considered a crucial driver of satellite internet development, attracting attention from academia and industry. On the other hand, with increasingly scarce radio spectrum resources, millimeter-wave communication offers greater bandwidth, providing opportunities for upgrading mobile communication systems and is thus widely regarded as a key technology for expanding the capacity of next-generation mobile networks. The development of optical millimeter-wave generation technology has not only propelled millimeter-wave communication systems towards lightweight and high-bandwidth designs but has also created possibilities for combining FSO with millimeter waves. Among these, optical heterodyne technology offers advantages such as avoiding the effects of light dispersion and the ability to flexibly generate millimeter-wave electrical signals of various frequencies. Furthermore, the fact that optical heterodyne technology does not require the introduction of a radio frequency source when generating millimeter-wave electrical signals is more conducive to promoting system lightweighting, making it a research hotspot in recent years.

[0003] In various application scenarios, both FSO and millimeter wave are effective wireless communication solutions with high capacity, offering complementary advantages in channel characteristics. In FSO systems, optical signals are easily affected by atmospheric turbulence when traversing the atmosphere, and fog is also one of the main factors affecting the transmission quality of FSO signals. In contrast, millimeter wave signals are less sensitive to atmospheric turbulence and fog, thus exhibiting greater stability in these aspects; however, millimeter wave electrical signals are significantly affected by raindrops. The complementary channel characteristics of these two technologies have led to their integration in practical applications, forming a more extensive and efficient communication solution, thereby improving the overall performance and reliability of the system. Currently, in traditional integrated transmission systems, the optical and millimeter wave links have redundant device functions at the transmitting and receiving ends, resulting in low structural integration, which is detrimental to the application of integrated transmission in space-based and airborne networks. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a bidirectional transmission system and method for optical and millimeter-wave fusion based on optical heterodyne, which generates single-sideband optical signals by means of optical heterodyne method, provides carrier-loaded single-sideband for space optical links and millimeter-wave links, realizes the multiplexing of related devices between the transmitters and receivers of the two links, and between the receiver of the space optical link and the transmitter of the millimeter-wave link, thereby reducing the structural complexity of the fused bidirectional system.

[0005] To achieve the above objectives, one aspect of the present invention provides a bidirectional transmission system for optical and millimeter-wave fusion based on optical heterodyne, the system including a transmission link in a first direction and a transmission link in a second direction, the two transmission links having the same link structure.

[0006] The link structure includes a signal transmitting end and a signal receiving end. The signal transmitting end includes a signal modulation unit for generating a single-sideband optical signal, a millimeter-wave generating unit for generating a millimeter-wave electrical signal, and an optical switch. One end of the optical switch is connected to the signal modulation unit, and the other end is used to select either a space optical antenna or the millimeter-wave generating unit. The signal receiving end includes an electrical switch and a demodulation unit connected to the electrical switch for demodulating the millimeter-wave electrical signal.

[0007] In the first direction of the transmission link, the signal transmitting end selects either a space optical link or a millimeter-wave link for signal transmission via an optical switch, and the millimeter-wave generating unit of the signal transmitting end is connected to the electrical switch of the receiving end in the second direction of the transmission link.

[0008] In the second direction of the transmission link, the signal transmitting end selects either a space optical link or a millimeter-wave link for signal transmission via an optical switch, and the millimeter-wave generating unit of the signal transmitting end is connected to the electrical switch of the receiving end in the first direction of the transmission link.

[0009] Furthermore, the signal modulation unit includes a pulse generator, a Mach-Zehnder modulator, a first laser source, and a second laser source. The pulse generator receives source codewords and generates pulse signals; the Mach-Zehnder modulator receives the pulse signals and the optical signals output from the first laser source for information loading; the optical signals output from the second laser source and the optical signals output from the Mach-Zehnder modulator are frequency-domain superimposed to form a single-sideband optical signal. The first and second laser sources output optical signals of different wavelengths.

[0010] Furthermore, the millimeter-wave generation unit includes a combiner, a photodetector, and a bandpass filter. The input of the combiner is connected to an optical switch, receiving the single-sideband optical signal output from the signal modulation unit; the input of the photodetector is connected to the output of the combiner; the input of the bandpass filter is connected to the output of the photodetector, and the output of the bandpass filter outputs a millimeter-wave electrical signal. In addition, the input of the combiner in the first direction transmission link also receives optical signals transmitted from the spatial optical link of the second direction transmission link; the input of the combiner in the second direction transmission link also receives optical signals transmitted from the spatial optical link of the first direction transmission link.

[0011] Furthermore, the demodulation unit includes a square-law detector, a low-pass filter, and a decision unit. The input of the square-law detector is connected to an electrical switch; the input of the low-pass filter is connected to the output of the square-law detector; and the input of the decision unit is connected to the output of the low-pass filter. The decision unit performs digital signal processing (DSP) on the input signal to demodulate the source signal.

[0012] Another aspect of the present invention provides a bidirectional transmission method based on optical heterodyne fusion of light and millimeter waves. This method reduces the number of devices used and lowers the size of the transmission system by multiplexing devices in both the spatial optical link and the millimeter wave link in the first direction and the spatial optical link and the millimeter wave link in the second direction. The specific design is as follows:

[0013] At the transmitting end of any direction transmission link, a signal modulation unit is multiplexed as an optical signal generation unit for both the spatial optical link and the millimeter-wave link in that direction, to generate a single-sideband optical signal.

[0014] At the receiving end of the transmission link in any direction, a demodulation unit is multiplexed as the receiving end of the space optical link and the millimeter-wave link in that direction. The demodulation unit selects to receive the millimeter-wave electrical signal transmitted by the millimeter-wave link in that direction or the space optical signal transmitted by the space optical link in the other direction through an electrical switch.

[0015] In both the first and second direction transmission links, a millimeter-wave generation unit is provided, which is multiplexed as both the receiver and transmitter of the space optical link. In either direction, for example in the first direction, the millimeter-wave generation unit receives the single-sideband optical signal from the signal modulation unit in the first direction via an optical switch. Simultaneously, it receives the space optical signal transmitted from the space optical link in the second direction, converts it into a millimeter-wave electrical signal, and transmits it to the demodulation unit at the receiver in the second direction for signal demodulation.

[0016] The first and second transmission directions can use the same type of link or different types of links through the configured optical and electrical switches. When the two transmission directions use the same type of link (space optical link or millimeter-wave link), the system is in homogeneous bidirectional transmission mode. Since the two links do not operate simultaneously, the photodetector and bandpass filter can be time-division multiplexed between the two links. When the two transmission directions use different types of links (i.e., one direction is a space optical link and the other is a millimeter-wave link), the system is in heterogeneous bidirectional transmission mode.

[0017] In heterogeneous bidirectional transmission mode, millimeter-wave generation units in both directions simultaneously receive single-sideband optical signals from the signal modulation unit and spatial optical signals from the spatial optical link. To avoid signal crosstalk caused by the multiplexing of photodetectors and bandpass filters in the two links, the two signals need to be decoupled using a priori information method. Specifically, in heterogeneous bidirectional transmission mode, the wavelength difference between the first and second laser sources in the signal modulation units of the first and second directions is the same.

[0018] The specific ways to avoid signal crosstalk are as follows:

[0019] Define the optical field of a single-sideband optical signal in a space optical link and the optical field of a single-sideband optical signal in a millimeter-wave link as follows:

[0020]

[0021] In the formula, S1(t), ω1, ω2, and θ1(t) represent the amplitude information of the left band of E1, the carrier frequency of the left band, the carrier frequency of the right band, and the phase information of the left band, respectively. S2(t), ω1, ω2, and θ2(t) represent the amplitude information of the left band of E2, the carrier frequency of the left band, the carrier frequency of the right band, and the phase information of the left band, respectively.

[0022] The superimposed optical signals enter the photodetector and beat frequency occurs. The electrical signal generated after beating frequency is:

[0023] I = 2[S1(t) + S2(t)] 2 +[S1(t)+S2(t)] 2 cos[(ω11-ω2)t]

[0024] In this equation, the first half of the right-hand side represents the generated baseband electrical signal, and the second half represents the millimeter-wave electrical signal with mixed information. After passing through a bandpass filter with a center frequency of |ω1-ω2|, the millimeter-wave electrical signal with mixed information and a center frequency of |ω1-ω2| is retained.

[0025] I hybrid-MMW = [S1(t) + S2(t)] 2cos[(ω1-ω2)t]

[0026] The hybrid millimeter-wave electrical signal obtained through a bandpass filter is divided into two parts. One part is processed by DSP at the receiver of the millimeter-wave link, and the other part is transmitted at the transmitter of the space optical link. According to the expression for the hybrid millimeter-wave electrical signal, there is a certain relationship between the amplitude of the hybrid millimeter-wave electrical signal and the amplitudes of the optical signals in the space optical link and the millimeter-wave link. Using a priori information method, the hybrid information is separated, and the signal information in these two links is reconstructed separately.

[0027]

[0028] Among them, S konwn H(t) is the known signal on one side of the two-way system, and H(t) is the channel response obtained by channel estimation based on the known signal.

[0029] The beneficial effects of this invention are as follows: This invention uses two laser sources of different wavelengths to generate single-sideband optical signals and utilizes a millimeter-wave transducer (MZM) to modulate the signals onto the light, enabling the space optical link and millimeter-wave link to reuse laser sources and MZM devices at the transmitting end. At the receiving end, both the space optical link and the millimeter-wave link undergo a series of processes such as square-law detection, low-pass filtering, and symbol decision, thus allowing the reuse of related electrical domain devices. This invention allows for the reuse of photodetectors and bandpass filters in both the time and frequency domains for the receiving end of the space optical link and the transmitting end of the millimeter-wave link. This invention solves the problems of functional redundancy, low structural integration, and hindering the development of space and airborne network communication in traditional hybrid transmission systems.

[0030] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0032] Figure 1 This is a structural diagram of a two-way transmission system based on optical heterodyne and millimeter wave fusion provided in an embodiment of the present invention;

[0033] Figure 2 The structure is that of a traditional two-way transmission system for light and millimeter waves. Figure 2 (a) is an FSO link. Figure 2(b) is a millimeter-wave link;

[0034] Figure 3 This diagram illustrates the average bit error rate of the FSO link under heterogeneous bidirectional transmission with varying received optical power.

[0035] Figure 4 This diagram illustrates the average bit error rate of the millimeter-wave link under heterogeneous bidirectional transmission with varying signal-to-noise ratio.

[0036] Figure 5 This diagram illustrates the average bit error rate of the FSO link under homogeneous bidirectional transmission.

[0037] Figure 6 This diagram illustrates the average bit error rate of the millimeter-wave link under homogeneous bidirectional transmission with varying signal-to-noise ratio. Detailed Implementation

[0038] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0039] like Figure 2 As shown, traditional optical and millimeter-wave bidirectional transmission systems mainly consist of FSO links and millimeter-wave links. Figure 2 (a) illustrates the FSO link in a bidirectional transmission system. Figure 2 (b) illustrates a millimeter-wave link in a conventional bidirectional transmission system. Figure 2 (a) Deploying the forward and backward directions can form a traditional FSO bidirectional transmission system. Figure 2 (b) Deploying the optical and millimeter-wave transmission links in both forward and backward directions can constitute a traditional millimeter-wave bidirectional transmission system. However, these traditional hybrid transmission systems suffer from redundant device functions at the transmitting and receiving ends of the optical and millimeter-wave links, resulting in low structural integration and hindering the development of space and air network communications.

[0040] Therefore, this invention proposes a fusion bidirectional transmission system based on optical heterodyne, integrating optical and millimeter-wave transmission. This system reduces the structural complexity of the fusion bidirectional system by multiplexing related devices between the transmitters of the two links (space light and millimeter-wave), between the receivers of the two links, and between the receiver of the space light link and the transmitter of the millimeter-wave link. The fusion bidirectional system constructed based on this three-level multiplexing design can be further divided into homogeneous bidirectional transmission and heterogeneous bidirectional transmission, depending on whether the link types used for bidirectional transmission are the same, to meet specific application purposes. In the case of homogeneous bidirectional transmission, the photodetector is shared in the time domain. In the case of heterogeneous bidirectional transmission, the two optical signals sharing the photodetector completely overlap in the frequency domain and can be decomposed using prior information.

[0041] Specifically, such as Figure 1 The diagram illustrates a bidirectional optical and millimeter-wave fusion transmission system according to an embodiment of the present invention. In this system, the transmitting end of the space optical link and the transmitting end of the millimeter-wave link multiplex laser sources and MZM devices; the receiving ends of the two links multiplex square-law detectors, low-pass filters, and symbol decision devices; and the receiving end of the space optical link and the transmitting end of the millimeter-wave link multiplex photodetectors and bandpass filters. In homogeneous bidirectional transmission mode, since the space optical link and the millimeter-wave link do not operate simultaneously in the two transmission directions, the photodetectors and bandpass filters can be time-division multiplexed. In heterogeneous bidirectional transmission mode, the single-sideband optical signals of the space optical link and the millimeter-wave link pass through the photodetector simultaneously, and are completely aliased in the frequency domain. Because in heterogeneous bidirectional transmission mode, one side integrates the millimeter-wave transmitting end and the space optical receiving end, and the other side integrates the millimeter-wave receiving end and the space optical transmitting end, and both transmitting ends record the transmitted symbol information, the receiving ends on both sides can extract the effective signal from the aliased signal of the photodetector using the prior features of the symbol information.

[0042] Based on the parameter settings in Table 1, an optical-millimeter wave hybrid bidirectional transmission system, a traditional optical-millimeter wave hybrid bidirectional transmission system, an FSO bidirectional transmission system, and a millimeter wave bidirectional transmission system were constructed through experiments, and the system performance was compared and analyzed.

[0043] Table 1

[0044]

[0045] Figure 3The figure shows the average bit error rate (BER) of the FSO link in two bidirectional transmission systems under heterogeneous bidirectional transmission mode as a function of received optical power. It can be observed that the average BER of the FSO link in both systems gradually decreases with increasing received optical power. In the fused bidirectional transmission system proposed in this invention, the average BER reaches the FEC threshold when the received optical power is approximately -6.4 dBm; while in the conventional bidirectional transmission system, the average BER also reaches the FEC threshold when atmospheric attenuation reaches -6.8 dBm. Under the same received optical power conditions, the difference in the average BER of the FSO link between the two bidirectional transmission systems is small. Figure 4 The figure shows the average bit error rate (BER) of the MMW link in heterogeneous bidirectional transmission mode for two bidirectional transmission systems as a function of signal-to-noise ratio (SNR). When the SNR of the integrated bidirectional transmission system proposed in this invention is approximately 18.8 dB, the average BER reaches the FEC threshold; while the traditional bidirectional transmission system reaches the corresponding FEC threshold at an SNR of approximately 18.3 dB. Under the same SNR, the average BER of the MMW link in the two systems exhibits relatively consistent characteristics. Furthermore, Figure 5 This demonstrates the average bit error rate of the FSO link in both systems under homogeneous bidirectional transmission, as the received optical power varies. From Figure 5 It can be seen that the average bit error rate of the FSO link in both systems changes in a basically consistent manner during the process of changing the received optical power. Figure 6 The average bit error rate (BER) of the MMW link in both systems varies with the signal-to-noise ratio (SNR) under homogeneous bidirectional transmission. It can be seen that, under the same SNR conditions, the average BER of the MMW link in both systems exhibits similar characteristics. These results demonstrate that, while saving a significant number of components, the system architecture of this invention can realize both homogeneous and heterogeneous bidirectional transmission, while maintaining performance close to that of conventional systems.

[0046] In summary, this invention utilizes an FSO analog transmission system with optical heterodyne generation of single-sideband and an optically generated millimeter-wave system to multiplex related devices between the transmitters of two links, between the receivers of two links, and between the receiver of the space optical link and the transmitter of the millimeter-wave link, thereby reducing the structural complexity of the fused bidirectional system. The fused bidirectional system constructed based on the three-level multiplexing design can be further divided into homogeneous bidirectional transmission and heterogeneous bidirectional transmission, depending on whether the link types used for bidirectional transmission are the same, to meet specific application purposes. In the case of homogeneous bidirectional transmission, the photodetector is shared in the time domain. In the case of heterogeneous bidirectional transmission, the two optical signals sharing the photodetector completely overlap in the frequency domain and can be decomposed using prior information.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A bidirectional transmission system for optical and millimeter-wave fusion based on optical heterodyne, characterized in that, The system includes a transmission link in the first direction and a transmission link in the second direction, and the transmission links in both directions have the same link structure; The link structure includes a signal transmitting end and a signal receiving end; the signal transmitting end includes a signal modulation unit for generating a single-sideband optical signal, a millimeter-wave generating unit for generating a millimeter-wave electrical signal, and an optical switch, one end of which is connected to the signal modulation unit, and the other end is used to select a space optical antenna or a millimeter-wave generating unit; the signal receiving end includes an electrical switch and a demodulation unit connected to the electrical switch for demodulating the millimeter-wave electrical signal; In the first direction of the transmission link, the signal transmitting end selects a space optical link or a millimeter wave link for signal transmission through an optical switch, and the millimeter wave generating unit of the signal transmitting end is connected to the electrical switch of the receiving end in the second direction of the transmission link. In the second direction of the transmission link, the signal transmitting end selects a space optical link or a millimeter wave link for signal transmission through an optical switch, and the millimeter wave generating unit of the signal transmitting end is connected to the electrical switch of the receiving end in the first direction of the transmission link. The signal modulation unit includes a pulse generator, a Mach-Zehnder modulator, a first laser source, and a second laser source; the pulse generator receives source codewords and generates pulse signals; the Mach-Zehnder modulator receives the pulse signals and the optical signals output from the first laser source for information loading; the optical signals output from the second laser source and the optical signals output from the Mach-Zehnder modulator are frequency-domain superimposed to form a single-sideband optical signal. The first laser source and the second laser source output optical signals of different wavelengths; and when the first direction and the second direction are transmitted using different links, the wavelength difference between the first laser source and the second laser source is the same in the signal modulation units of the two directions. The millimeter-wave generation unit includes a combiner, a photodetector, and a bandpass filter. The input of the combiner is connected to the optical switch and receives a single-sideband optical signal output by the signal modulation unit. The input of the photodetector is connected to the output of the combiner. The input of the bandpass filter is connected to the output of the photodetector, and the output of the bandpass filter outputs a millimeter-wave electrical signal. Furthermore, the input of the combiner in the first direction transmission link also receives an optical signal transmitted from the spatial optical link of the second direction transmission link; the input of the combiner in the second direction transmission link also receives an optical signal transmitted from the spatial optical link of the first direction transmission link. When the millimeter-wave generation unit simultaneously receives a single-sideband optical signal from the signal modulation unit and a space optical signal from the space optical link, it decouples the two signals using a priori information method to avoid signal crosstalk: for the single-sideband optical signal field in the space optical link... Single-sideband optical signal field in millimeter-wave links When the two optical signals are superimposed, they enter the photodetector and beat frequency occurs. The electrical signal generated after beating frequency is: In the formula, , , They are The amplitude information on the left side, the carrier frequency on the left side, and the carrier frequency on the right side; yes The left side contains amplitude information; the first term on the right side of the equals sign is the generated baseband electrical signal, and the second term is the millimeter-wave electrical signal with mixed information; With center frequency After applying the bandpass filter, the center frequency is obtained as Millimeter-wave electrical signals with mixed information: By using prior information, the mixed information is separated, and the signal information in these two links is reconstructed separately: In the formula, This represents a known signal on one side of the system. This is the channel response obtained by channel estimation based on known signals.

2. The system according to claim 1, characterized in that, The demodulation unit includes a square-law detector, a low-pass filter, and a decision unit; the input of the square-law detector is connected to the electrical switch; the input of the low-pass filter is connected to the output of the square-law detector; the input of the decision unit is connected to the output of the low-pass filter, and the output of the decision unit outputs the demodulated signal.

3. A bidirectional transmission method for light and millimeter-wave fusion based on optical heterodyne, characterized in that, This method reduces the number of devices and lowers the size of the transmission system by multiplexing devices in the space optical link and millimeter-wave link in the first direction and the space optical link and millimeter-wave link in the second direction, including: At the transmitting end of any direction transmission link, a signal modulation unit is multiplexed as an optical signal generation unit for both the spatial optical link and the millimeter-wave link in that direction, to generate a single-sideband optical signal. At the receiving end of any direction transmission link, a demodulation unit is multiplexed as the receiving end of the space optical link and the millimeter wave link in that direction. The demodulation unit selects to receive the millimeter wave electrical signal transmitted by the millimeter wave link in that direction or the space optical signal transmitted by the space optical link in that direction through an electrical switch. In both the first and second direction transmission links, a millimeter-wave generation unit is provided. This millimeter-wave generation unit is multiplexed to receive spatial optical signals from the spatial optical link and to generate millimeter-wave signals for the millimeter-wave link. In either direction, the millimeter-wave generation unit receives a single-sideband optical signal from the signal modulation unit in that direction through an optical switch, converts it into a millimeter-wave signal, and then transmits it to the millimeter-wave link in that direction for transmission. Simultaneously, it receives spatial optical signals transmitted from the spatial optical link in the other direction, converts them into millimeter-wave electrical signals, and then transmits them to the demodulation unit at the receiving end in the other direction for signal demodulation. In the signal modulation unit, a laser source is used to generate an optical signal and a Mach-Zehnder modulator is used to load information; another laser source with a different wavelength is used to generate an unmodulated optical signal, and the unmodulated optical signal and the optical signal loaded with information are superimposed in the frequency domain to form a single-sideband optical signal. The millimeter-wave generation unit includes a combiner, a photodetector, and a bandpass filter; the input of the combiner is connected to the optical switch and receives the single-sideband optical signal output by the signal modulation unit; the input of the photodetector is connected to the output of the combiner; the input of the bandpass filter is connected to the output of the photodetector, and the output of the bandpass filter outputs a millimeter-wave electrical signal; wherein, the combiner simultaneously receives space optical signals transmitted from a space optical link; When transmission occurs via a space optical link in one direction and a millimeter-wave link in the other, the millimeter-wave generation units in both directions simultaneously receive a single-sideband optical signal from the signal modulation unit and a space optical signal from the space optical link. The single-sideband and space optical signals are then superimposed by a combiner. At this point, the two signals need to be decoupled using prior information to avoid crosstalk. Methods to avoid crosstalk include: for the single-sideband optical signal field in the space optical link... Single-sideband optical signal field in millimeter-wave links When the two optical signals are superimposed, they enter the photodetector and beat frequency occurs. The electrical signal generated after beating frequency is: In the formula, , , They are The amplitude information on the left side, the carrier frequency on the left side, and the carrier frequency on the right side; yes The left side contains amplitude information; the first term on the right side of the equals sign is the generated baseband electrical signal, and the second term is the millimeter-wave electrical signal with mixed information; With center frequency After applying the bandpass filter, the center frequency is obtained as Millimeter-wave electrical signals with mixed information: By using prior information, the mixed information is separated, and the signal information in these two links is reconstructed separately: In the formula, This represents a known signal on one side of the system. The channel response is obtained by channel estimation based on known signals; In this method, when one direction is transmitted via a spatial optical link and the other direction is transmitted via a millimeter-wave link, the wavelength difference between the first laser source and the second laser source is the same in the signal modulation units of the two directions.

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